Wheel bearing apparatus is generally known which supports a vehicle wheel relative to a suspension apparatus and which incorporates a wheel speed detecting apparatus to detect rotational speed of the vehicle wheel. The detecting apparatus detects the wheel speed to control the anti-lock braking system (ABS). Such a bearing apparatus generally includes a wheel speed detecting apparatus with a magnetic encoder. The encoder has magnetic poles alternately arranged along its circumferential direction. The magnets are integrated in a sealing apparatus arranged between inner and outer members to contain rolling elements (balls or rollers). A wheel speed detecting sensor detects the variation in the magnetic poles of the magnetic encoder according to the rotation of the wheel.
The wheel speed sensor is usually mounted on a knuckle after the wheel bearing apparatus has been mounted on the knuckle to form a suspension apparatus. Wheel bearing apparatus with a wheel speed detecting apparatus have recently been proposed where a wheel speed detecting sensor is self-contained within the wheel bearing. This reduces the size of the wheel bearing apparatus as well as eliminates troublesome in air gap adjustment between the wheel speed sensor and the magnetic encoder.
An example of a wheel bearing apparatus with a wheel speed detecting apparatus known in the prior art (e.g. Japanese Laid-open Patent Publication No. 2003-254985) is shown in FIG. 5. This wheel bearing apparatus with a wheel speed detecting apparatus includes an outer member 51 which forms a stationary member secured on a suspension apparatus (not shown). An inner member 52, which includes a wheel hub 55 and an inner ring 56, is inserted into the outer member 51 via double row rolling elements (balls) 53 and 53 therebetween. The outer member 51 has an integrally formed wheel mounting flange at one end and double row outer raceway surfaces 51a and 51a formed on its inner circumferential surface. The inner member 52 has double row inner raceway surfaces 55a and 56a opposite to the double row outer raceway surfaces 51a and 51a. One (55a) of the double row inner raceway surfaces is formed on the outer circumferential surface of the wheel hub 55. The other (56a) is formed on the outer circumferential surface of the inner ring 6. The inner ring is press-fit on the hub cylindrical portion 55b extending axially away from the inner raceway surface 55a of the wheel hub 55. Double row rolling elements 53 and 53, held by cages 57, 57, are arranged between the outer and inner raceway surfaces 51a and 51a; 55a and 56a, respectively.
The wheel hub 55 has an integrally formed wheel mounting flange 54 to mount a wheel (not shown). Hub bolts 54a, to secure the wheel, are rigidly secured on the wheel mount flange 54 at an equidistant along its periphery. A serration 55c is formed on the inner circumferential surface of the wheel hub 55. A stem portion 61 of an outer joint member 60, which forms a part of a constant velocity universal joint (not shown), is inserted into the wheel hub serration 55. Seals 58 and 59 are arranged at both ends of the outer member 51 to prevent leakage of grease contained within the bearing as well as ingress of rain water or dust into the bearing.
The seal 59 on the inboard side, as shown in an enlarged view of FIG. 6, is fit into the inner circumference at the end of the outer member 51. The seal 59 includes a first sealing plate 62 and a second sealing plate 63 having a “L”-shaped cross-section. The second sealing plate 63 has a cylindrical portion 63a fit onto the outer circumference of the inner ring 56. A standing portion 63b extends radially outward from the cylindrical portion 63a. A magnetic encoder 64 is adhered, via vulcanized adhesion, on the outer surface of the standing portion 63b. The magnetic encoder 64 is formed from a rubber magnet in which magnetic N and S poles are alternately arranged along the circumferential direction.
The first sealing plate 62 includes a metal core 65 having a substantially “L”-shaped cross-section. A sealing member 66, including a side lip 66a, is in sliding contact with the inner side surface of the standing portion 63b of the second sealing plate 63. A pair of radial lips 66b and 66c is in sliding contact with the cylindrical portion 63a of the second sealing plate 63.
An annular sensor holder 69 is mounted on one end of the outer member 51. The annular sensor holder 69 includes a fitting cylinder 67 and a holding portion 68 connected to the fitting cylinder 67. The fitting cylinder 67 has an annular configuration with an “L”-shaped cross-section. The fitting cylinder 67 includes a cylindrical portion 67a and a flange portion 67b, which extends radially inward from the cylindrical portion 67a. 
The holding portion 68 is made from synthetic resin molded into an annular body. A wheel speed sensor 70 is embedded into the resin. The wheel speed sensor 70 is arranged opposite to a magnetic encoder 64 with a predetermined air gap between the two. The wheel speed sensor 70 includes a magnetic detecting element, such as a Hall element, a magnetic resistance element (MR element) etc., which changes characteristics in accordance with the flowing direction of the magnetic flux. Also included is an IC with a waveform shaping circuit to shape the output waveform of the magnetic detecting element.
A labyrinth seal is formed by a small gap 71 arranged between the flange portion 67b of the fitting cylinder 67 and the opposed end surface of the inner ring 56. The seal prevents ingress of foreign matter, such as magnetic powder, into a space between the magnetic encoder 64 and the detecting portion of the wheel speed sensor 70 from outside of the bearing apparatus and before the stem portion 61 of the outer joint member 60 is inserted into the wheel hub 55, which includes a course where the bearing apparatus is transferred to an assemble line of an automobile manufacturer. Accordingly, this improves the detecting reliability of the rotational speed of the wheel.
Although the wheel bearing apparatus incorporated with a wheel speed detecting apparatus of the prior art has superior effects mentioned above, it is impossible to prevent ingress of foreign matter, such as magnetic powder, into a space between the magnetic encoder 64 and the detecting portion of the wheel speed sensor 70 from outside of the bearing apparatus and under severe circumstances during real running of the vehicle.